The invention relates to an arrangement and to a method for simultaneous polyfocal imaging of the surface profile of any desired objects, in particular for measuring the surface profile of teeth, having a light source for illuminating the object, having optics for focusing the light signals returning from the surface of the object, having a detector which records the light signals, and having a processor which digitizes and further-processes the detected signals. The invention also relates to a particular application of the arrangement according to the invention for reading and writing digital or binary information from an optical data medium and, respectively, to an optical data medium.
In principle, the invention relates to an arrangement and to a method for measuring surfaces of any type and of any contour, to be precise using a technique known from confocal microscopy. Various arrangements and methods for surface measurement are already known from practical experience.
Thus, for example, a light section sensor can be used to project a light line onto the object, and a CCD camera can be used to observe it, at an angle. The geometrical deformation of the light line is in this case measured. The height differences on the object are calculated from this deformation. By shifting the object under the sensor--at right angles to the light line--and by repeatedly measuring a profile, the surface shape can be measured or determined in a serial manner.
The light section sensor is admittedly a sensor of simple design and is robust, but the oblique illumination required here leads to shadowing on one side of steep points. This results in asymmetries in the imaging and inaccuracies. Furthermore, the measurements are sometimes inaccurate or corrupted owing to light being scattered from various depths, for example, on at least partially transparent tooth material.
Furthermore, it is also already known from practical experience for surfaces to be scanned by means of confocal microscopy and for this to be used to generate three-dimensional records of the surface. For this purpose, reference is made, only by way of example, to J. Engelhardt and W. Knebel in "Konfokale Laserscanning-Mikroskopie" [Confocal laser scanning microscopy] Physik in unserer Zeit [Physics Today], Jan. 24, 1993, No. 2, pages 70-78 and D. K. Hamilton and T. Wilson in "Three-Dimensional Surface Measurement Using the Confocal Scanning Microscope" Applied Physics B,27: 211-213 (1982).
Confocal microscopy is particularly highly suitable for surface measurement of toothed surfaces since, according to this method, the only structures that are imaged are those which are located directly in the focal plane of the microscope objective. Measurement errors resulting from partially transparent tooth material are thus effectively prevented. However, conventional confocal microscopes corresponding to the prior art have a very considerable physical size owing to their universal nature, so that they are not suitable for polyfocal imaging of the surface profile of widely differing objects, for example for measuring the surface profile of teeth, owing to their physical size. Furthermore, conventional confocal microscopes have a design that is too complicated for numerous simple applications, such as pure profile measurement, and are thus much too expensive.